Coolant system for heat removal apparatus

ABSTRACT

A system and apparatus is provided for continuous coolant of products such as food products with liquid refrigerants which apparatus minimizes atmospheric contamination with gaseous refrigerant and is useful in the recovery of the condensable, normally gaseous refrigerant. The apparatus comprises a cooling chamber having inlet and outlet vestibules, conveying means for transporting products such as food products through the cooling chamber via the vestibules, means for applying and distributing refrigerant in liquid form to the food product while in said chamber, recovery traps associated with the vestibules for gravitational recovery of gaseous refrigerant, conduits leading from the traps to recirculate the gaseous refrigerant to a compressor, means for compression and liquification of the gaseous refrigerant and conduit means for conducting liquified refrigerant to the distributing means. A process for the cooling of food or other products is also provided which comprises passing units of product to be cooled in a continuous stream through a cooling zone chamber, provided with inlet and outlet vestibules, applying liquid refrigerant to products in the chamber, which refrigerant is normally gaseous and heavier than air at ambient operating temperatures, to thereby reduce the temperature of the produce, regulating the rate of introduction of refrigerant into said chamber to provide a slight positive refrigerant gas pressure in said chamber, recovering the gaseous refrigerant at inlet and outlet vestibules by gravitational separation from atmospheric air, liquifying the gaseous refrigerant and recycling the liquified refrigerant in the process.

United States Patent 91 Schmidt [451 Apr,24, l973 COOLANT SYSTEM FOR HEAT REMOVAL APPARATUS Harry Schmidt, 20 North Wacher Drive, Chicago, 111. 60606 [22] Filed: Dec. 27, 1971 [21] Appl. No.: 211,933

[76] Inventor:

[56] References Cited UNITED STATES PATENTS 2,015,167 9/1935 Varney ..62/63 2,059,970 11/1936 Robillard .62/63 3,368,363 2/1968 Alaburda et ul,, 62/64 3,369,371 2/1968 Holly et a1. 62/54 3,413,818 12/1968 Pelmulder 62/63 3,507,128 4/1970 Murphy et a1. ...62/63 3,605,427 9/ l 971 Rudy ..62/64 Primary ExaminerWilliam F. ODea Assistant ExaminerRonald C. Capossela AttorneyAlbert H. Pendleton et a1.

[5 7] ABSTRACT A system and apparatus is provided for continuous coolant of products such as food products with liquid 32 TD DER/N 9 refrigerants which apparatus minimizes atmospheric contamination with gaseous refrigerant and is useful in the recovery of the condensable, normally gaseous refrigerant. The apparatus comprises a cooling chamber having inlet and outlet vestibules, conveying means for transporting products such as food products through the cooling chamber via the vestibules, means for applying and distributing refrigerant in liquid form to the food product while in said chamber, recovery traps associated with the vestibules for gravitational recovery of gaseous refrigerant, conduits leading from the traps to recirculate the gaseous refrigerant to a compressor, means for compression and liquification of the gaseous refrigerant and conduit means for conducting liquified refrigerant to the distributing means.

A process for the cooling of food or other products is also provided which comprises passing units of product to be cooled in a continuous stream through a cooling zone chamber, provided with inlet and outlet vestibules, applying liquid refrigerant to products in the chamber, which refrigerant is normally gaseous and heavier than air at ambient operating temperatures, to thereby reduce the temperature of the produce, regulating the rate of introduction of refrigerant into said chamber to provide a slight positive refrigerant gas pressure in said chamber, recovering the gaseous refrigerant at inlet and outlet vestibules by gravitational separation from atmospheric air, liquifying the gaseous refrigerant and recycling the liquified refrigerant in the process.

11 Claims, 1 Drawing Figure COOLANT SYSTEM FOR HEAT REMOVAL APPARATUS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to refrigeration system apparatus and processes for cooling products with a cold liquid form of normally gaseous refrigerant material.

2. Description of the Prior Art The prior art processes for direct contact refrigera tion have not acquired broad use. The procedures normally employed in the past were processes which involved the cooling or food or other products wherein a I liquified refrigerant material contacts a product in a closed chamber or a vat, vaporizes and concomitantly reduces the product in temperature by removal of the quantity of heat associated with the latent heat of vaporization for the particular refrigerant employed. The refrigerant gases normally are vented to the atmosphere without attempt to recover and recycle. The refrigerant gas in some cases was obnoxious and represented a pollutant in the atmosphere. Furthermore, the operation resulted in cold draft problems from spillover of gases as well as a respiratory hazard to workers. Obviously, the loss of refrigerant adds to the cost of the operation and prevents this type of system from enjoying any widespread use.

In those cases where a continuous process or system is employed, attempts to recover gases for recycle and reliquification were not commercially successful.

Of course, the conventional continuous cooling and refrigeration techniques of products such as foods which involve blast cooling (cold air) or radiation cooling are still practiced and in some cases on a production line basis. These systems, however, are not as effective or rapid as liquid refrigerant, direct contact cooling, and require a longer process time and much larger equipment space for a given production volume.

BRIEF SUMMARY OF THE INVENTION The present invention relates to an apparatus for cooling product by contact with a liquified, normally gaseous refrigerant, which apparatus in one broad form comprises, a cooling chamber having a portal for introduction and removal of products; a cooling zone within said chamber for contacting said products with liquid refrigerant; means for introducing liquifie'd refrigerant into said cooling zone; conveyor means for conveying products into and out of said chamber and said cooling zone; trap means adjacent to and cooperating with said portal for recovering heavierthan-air gaseous refrigerant and maintaining the same separated from atmospheric gases; compressor means for liquifying the gaseous refrigerant recovered in said trap and means for recirculating the refrigerant to said means for introducing the same into the cooling zone.

More particularly, this invention relates to an apparatus for the continuous cooling of products, such as food products, with liquid refrigerant which is normally gaseous and heavier-than-air at normal room temperatures and recovery of the refrigerant with minimal contamination of the atmosphere or the refrigerant which comprises:

a. a cooling chamber having inlet and outlet vestibule means for passage of food product into and out of the chamber;

b. conveyor means for passing food products through the cooling chamber via said vestibules; I c. application means for applying liquid refrigerant on conveyed food products in the chamber; d. recovery traps associated with said vestibules for recovery of heavier-than-air gaseous refrigerant;

e. conduit leading from said traps to a gas liquifying apparatus; and

f. conduit means for conducting liquified refrigerant to the application means.

A liquid refrigerant contact cooling process is also provided which comprises:

a. passing units of product'in a continuous stream through a confined cooling zone chamber; contacting the product units while in the confined zone with a chilled liquid refrigerant which is normally gaseous at room temperature to reduce the temperature of the food product by evaporative cooling;

. regulating the rate of introduction of refrigerant into said cooling zone chamber to provide the requisite cooling of product and maintain a slight positive pressure of gaseous refrigerant in said chamber;

. recovering the gaseous refrigerant by gravitational separation from atmospheric gases at the points of inlet and outlet of the product unit stream to the confined cooling zone;

conducting the recovered gaseous refrigerant to a liquification zone and liquifying the same; and

f. recycling the liquified refrigerant to the cooling zone.

In the process of the present invention, the refrigerant may be any typical refrigerant which is normally gaseous at ambient room temperatures but which may be readily liquified by compression and cooling. In the case of cooling and freezing of food products, refrigerants which are non-toxic and unreactive to the food, such a liquid nitrogen, carbon dioxide or freons are preferred. Exemplary of refrigerants which may be employed in cooling of non-food products are ammonia, carbon dioxide, sulfur dioxide, freon, or the like. Liquid nitrogen or carbon dioxide, because of their inert, non-toxic, non-explosive, non-polluting characteristic, is a preferred refrigerant, especially for food products.

While the present invention is especially adapted to cooling and freezing of food products, it should be understood that it also may be used to freeze or cool nonfood products such as pharmaceuticals, vitamins, blood, biologicals, metal parts such as shafts or axles on which heated gears or wheels are shrunk in a friction fit, rubber or plastic parts which must be rigiditied at low temperatures for machinery and the like.

The process and apparatus is adapted to recover refrigerants of the type described which are heavierthan-air. The recovery is by means of gas traps placed at the vestibules at the points of entry and .exit of the product units which pass on a conveyor through the chamber in a continuous stream.

The recovery of essentially uncontaminated gaseous refrigerant is accomplished by a gravitational separation in the gas trap and maintaining the refrigerant gas in the chamber at a slight positive pressure with respect to the atmosphere which is usually 14.7 psia.

The recovery of uncontaminated refrigerant is assisted by the gaseous refrigerant which sweeps the inlet and outlet vestibules in such a manner as to prevent ingress of the atmospheric gases which are considered as contaminants.

Means are also associated with the traps for collection of condensed moisture and melting of snow or the like and collecting the resulting moisture. The removal of moisture, of course, prevents that material from contaminating the gaseous refrigerant stream and requiring removal prior to recycle in the process.

The apparatus also permits the rapid evacuation of gases from the chamber to permit workmen to enter for repairs, maintenance or the like.

BRIEF DESCRIPTION OF THE DRAWING For a more complete understanding of the invention reference is made to the Drawing which is a diagra matic side elevational view of the apparatus and process flow sequence.

DETAILED DESCRIPTION OF THE INVENTION In the attached drawing, there is illustrated a side elevation, cut-away, diagramatic and schematic view of one form of the novel apparatus employed in practicing the process of the present invention, including a cooling chamber 12 provided with conveyor inlet and outlet ports 14 and 16 respectively and associated vestibules l8 and 20. A product conveying means 22 is also shown having a path of travel indicated by the arrows. The conveyor 22 may be a link belt or the like and the travel may be disposed as a single pass or to follow a circuitous route as shown in the drawing. The chamber 12 is box-like or tunnel-like in form and is illustrated in the drawing in the vertical position with 12a forming the base, walls 12b and 12c forming the sides, wall 12d thetop, and wall 12s the rear. The front wall of the chamber is not shown in the cut-away side elevational view.

' Associated with each vestibule is a trap 18a and 20a which is in the form of a trough or cup-like receptacle. Conduits or ducts 24 and 26 lead from the traps 18a and 20a respectively and conduct gases recovered from the traps to conduit 25, fan 27 and exhaust vent 28 or recycle conduit 30. Condensate drains 32 and 34 are provided in each trap to drain moisture, with associated drain lines 32a and 34a, with drain line heaters and check valves 32b, 32c, and 34b and 34c respectively. Heating means 32b and 34b maintain the liquidity of condensate (water) to assure free flowing and eliminate freezing of the valve and line. Other heating means such as heating cables or the like 32d and 34d serve to melt frost or snow on the inner walls of traps 18a and 20a. The vestibules l8 and 20 are formed by the baffle elements 101 and 102 in the form of removal panels which provide easy access to the vestibules and chamber, extending from the outer side walls 12b and 12c of the chamber 12 and above the trough-like trap element's 18a and 20 a. Front and rear walls are also provided for each vestibule of which the rear walls 18b and 20b only are shown. Doors 108 and 109 are provided to close off vestibules l8 and 20 during shut down.

Conduits or ducts 36 and 38 for carrying gaseous refrigerant are provided which terminate at 36a and 38a adjacent the ports 14 and 16 and are positioned to discharge refrigerant gas at termination points 36a and 38a into the vestibules 18 and 20. The conduits 36 and 38 join in common conduit 40 which leads to vaporizer chamber 60a. By-pass conduit 42 leads from conduit 40 to conduit 25 to either fan 27 and exhaust 28 or to gas recycle line 30.

A spray nozzle or other liquid refrigerant distribution means 44 provides for distributing liquid refrigerant onto the food or similar products indicated as 22a on conveyor 22 in chamber 12 causing them to be cooled or frozen as desired. The liquid refrigerant is conducted via line 46 to spray head 44 with intervening automatic flow regulating valves 48, strainer 50 (for ice or dirt particles), and manual shutoff valve 51. Line 46 is connected to source 52 through 4-way junction 52c and line 52a.

Line 52b carries liquid refrigerant from junction 52c and source 52 via valves 54 (manual), strainer 56, automatic flow control valve 58 to distribution, means 60 which dispenses liquid refrigerant to heating coils 62 in vaporizer chamber 60a. The coils 62 vaporize liquid refrigerant from 60 and the resulting vapor or gaseous refrigerant passes through conduit 40, conduits 36 and 38 to points 36a and 38a adjacent ports 14 and 16 of chamber 12. The heater element or coil 62 is heated by fluid supplied via inlet line 64 and return line 66. It should be understood that other heater means and heat sources may be employed in lieu of coil 60 described above. Valves (manual shut-off) 64a, and automatic flow control valve 66a, temperature controller 66b, flow rate transmitter 660, manual shut-off valve 66d, and manual flow control flow valve 66e control flow of fluid heating medium in this system.

A recycle system is provided which includes conduit 30 (fed by conduits 25, 24, 26 and 42) which conducts gaseous refrigerant to a compression and liquifying station 84. The cooling of the compressed refrigerant gas at 84 may be partially accomplished under certain thermal conditions by the use of effluent coolant in line 66 from vaporizer coil 62 which may be returned from station 84 as heated fluid in line 64 for recycle to coil 62', The liquified refrigerant from station 84 is recycled ,in the process via line 86 tojunction 52c and lines 46 and 52b for recycle in the process. The entire refrigerant recycle system may employ recycle through compressor 84 and source 52 would merely be for start-up or to supplement small losses of gaseous refrigerant to the atmosphere which, of course, would occur in normal operation.

Motor controlled dampers 68, 69, 70, 72 and 74 are provided to control flow of refrigerant gas in the conduits 24, 25, 26, 36, 38, 40, 42 and 80. The motors are designated as 684, 70a, 72a and 74a.

An exhaust fan 78 is connected to chamber 12 via conduit or duct 80 and passes gases to exit or atmosphere via conduit 80a.

Temperature control measures temperature in chamber 12, gas concentration meter 92 is provided to determine gas concentration in chamber 12. A draft gauge 94 measures pressure in the chamber. These units may be interconnected to the various flow control valves for automatic operation as will be more fully explained hereinafter.

In Operation, food or other product 22a on conveyor 22 passes into chamber 12. Cold, liquid refrigerant is distributed onto the food by nozzle 44 and the food is chilled or frozen by evaporation of the liquid refrigerant to the gaseous or vapor state. The food product enters at port 14 and is discharged in chilled or frozen state at port 16. During operation, additional liquid refrigerant from source 52 or compressor 84 may be vaporized by spraying from spray 60 onto coils 62 in chamber 60a. The gaseous or vaporized refrigerant passes via conduits 40, 38, and 36 to chamber 12 and discharges-adjacent ports 14 and 16. The gas volume generated in the chamber by vaporization of the liquid refrigerant sprayed on the food and that from lines 38 and 36 provides a positive pressure in chamber 12 only slightly above normal atmospheric pressure of 14.7 psia. Ordinarily, a pressure of up to about 0.2 inch above normal atmospheric pressure is adequate.

The refrigerant gas in chamber 12, being at a positive pressure slightly above atmospheric pressure, of course, tends to pass out ports 14 and 16. Being heavier-than-air, the refrigerant gas drops into and collects in traps 18a and 20a of the vestibules 18 and 20, and thence via collector or recovery conduits 24 and 26 to exhaust via conduit and fan 27 or recycle (condensation or liquification at 84) via conduit 30. In recycle, reliquified refrigerant gas from 84 is returned to the system via line 86 for reuse as described above. When gas is exhausted via fan 27, liquified refrigerant is obtained exclusively from source 52.

The positive pressurization of chamber 12 results in the outward flow of gaseous refrigerant through ports 14 and 16, preventing atmospheric gases from flowing into chamber 12 through ports 14 and 16; and the distinct separation caused by the heavier-than-air character of the gaseous refrigerant minimizes any substantial contamination by atmospheric gases or air in vestibules 18 and 20. As noted above, the heavy gaseous underlying refrigerant forms an interface with the overlying atmospheric air or gases which is indicated by the dotted lines 100 and 100a in vestibules 18 and 20. Of course, there will be some minor contamination so that after a period of time, the system will require purging and charging with fresh refrigerant gas. It is also possible that a certain amount of refrigerant will be lost from the process due to the absorbtion of other types of retention by the cooled product as it leaves chamber 12. However, the addition of a constant amount of fresh refrigerant from source 52 tends to reduce this problem since any losses of gas to the atmosphere are always of gas that contains contaminants and replacement is with pure refrigerant.

The control of the freezing operation is monitored by the temperature control 90, which measures conditions within the chamber 12. Temperature control 90 is preset to predetermined temperature and is connected to automatic flow control valve 48 which controls the flow of liquid refrigerant spray into chamber 12. The evaporation of the liquid refrigerant produces a volume of gaseous refrigerant in chamber 12. To maintain the necessary sweep of gas through the chamber and out of the ports 14 and 16 to the collection traps 18a and 20a and prevent ingress of atmospheric air into chamber 12, additional gaseous refrigerant may have to be supplied by vaporizer chamber 60a whenever the amount of gaseous refrigerant evaporated by the product heat is insufficient to create an adequate positive pressure in chamber 12. The total volume of gas passing out of chamber 12 to recovery should be such as very little or none is lost by spillover through doorways 108 and 109 from the traps 18a and 20a in vestibules 18 and 20.

The temperature control controls valves 48 and 58 in either a two-position or proportioning-modulation manner so that when valve 48 opens, valve 58 closes and the sum total of fluid passing through valves 48 and 58 remains constant and the gas in the system, of course, remains at the proper pressure levels and volume flows. Temperature control 90 also effects a reset of temperature control 1 10 to the temperature set at 90 so that vapor leaving chamber 60a will be at the temperature of chamber 12. Controller is coordinated with automatic flow control valve 66a which controls flow of heating fluid or heat energy through coil 62. Temperature controller 66b senses temperature of heating fluid return and if the fluid is water, brine or the like, and becomes too cold with the hazard of freeze-up, 66b closes valve 58 to reduce through-put to coil 62. If the flow rate of heating fluid in line 66 becomes too low as determined by flow measuring device 660, a flow rate transmitter will also cut off valve 58 to prevent excessive drop of temperature of heating fluid in line 66.

In start up, shut-down, or during operation gas concentration meter 92 determines the purity of the gaseous vapor in chamber 12. In the normal operation damper 68 is opened, and interconnected damper 69 is closed. At the same time dampers 70 and 74 for recycle are open; damper 72 is closed and fan 78 is inoperative.

In the event of a temporary shut-down, valve 48 is closed, dampers 68, 70 and 74 are closed, and dampers 69 and 72 are opened and fan 78 is activated by interconnection with 72. This exhausts all vapors in chamber 12 by pulling fresh air through ports 14 and 16.

In this shut-down procedure, gaseous refrigerant is continually generated at 600 but the gas passes through conduits 42, 25 and 30 to station 84 for reliquification and recycle to 60. This procedure, in effect, by-passes chamber 12 during the temporary shut-down of the freezing operation. After, the refrigerant gas has been removed from chamber 12, access may be had thereto when gas concentration meter 92 indicates a safe atmosphere in chamber 12 for human occupancy.

If a shut-down is for a more extended period, valves 51, 54, 58 and 640 are also closed, recycling system 84 or fan 27 are shut down, and no gas is generated in chamber 60a.

After correction of the problem, the chamber is reactivated by closing port doors 108 and 109, opening dampers 68, 70, 74, valve 48 and valves 51, 54, 58 and 64a, if necessary. Damper 72 is open and fan 78 continues to run drawing out air until temperature control 90, and gas concentration meter 92, indicate recharge of the system and deactivate fan 78. At that time port doors 108 and 109 are opened and the freezing of items on conveyor 22 recommences. At the time when fan 78 is deactivated, damper 72 is closed, fan 27 and/or recycling system is reactivated, if necessary, and the circulation of gaseous refrigerant is restarted from chamber 12 through the recycle operation or exhaust fan 27.

In operation condensate, in the form of water or snow, is formed during the freezing operation.- This tends to collect in traps 18a and 20a and is melted by heaters 32d and 34d and the water passes to drain via conduits 32a and 34a. The drain lines 32a and 34a have check valves 32c and 34c to prevent loss of gas or contamination by air and line heaters 32b and 34b to prevent freeze-up of condensate.

The apparatus and process described in the foregoing are eminently suitable for freezing or cooling of various products such as food products by direct contact freezing or cooling with liquid, normally gaseous refrigerants or cryogenic materials. Of course, modifications of the apparatus are possible which will permit carrying out of the cooling or freezing process and recovery and recycle of refrigerant without substantial contamination of the atmosphere through leakage.

For example, the conveyor 22 may ingress and exit through a single portal equipped with a vestibule and traps such as 18 and 18a which would also eliminate vestibule and trap 20 and 20a and conduit 38. Likewise, instead of distributor or spray head 44, the food or other products may be passed through a liquid bath of cryogenic material or refrigerant placed in chamber 12 and supplied via line 46 with appropriate level control systems for the vat containing the refrigerant bath. The other systems for recycle (84) and flow of gaseous refrigerant 60, 60a and 62 would remain in effect. Of course, this alternative embodiment would utilize a liquid refrigerant bath which may not be desired and in some cases would be more difficult to control.

It. should also be understood that while reference is made herein to compressor means used to liquify recycle refrigerant gases, that equivalent alternatives of gas liquifying systems which do not employ a compression step per se may also be employed in lieu thereof.

What is claimed is:

1. An apparatus for cooling of product units by contact with liquid refrigerant materials which are normally gaseous and heavier-than-air at ambient room temperature conditions in a cooling chamber which, under normal operation conditions, contains said refrigerant in gaseous form at a positive pressure with respect to the atmosphere which apparatus comprises:

a. a cooling chamber essentially closed to the atmosphere having at least one portal means for introduction and removal of product units, said chamber having direct communication to the surrounding atmosphere only at said portal means;

b. a cooling zone and refrigerant contact means within said chamber for contacting said products with liquid refrigerant;

c. means for introducing liquid refrigerant into said cooling zone and to said contact means;

. conveyor means for conveying products into and out of said chamber and cooling zone;

e. trough-like trap means located outside the cooling chamber adjacent to, below and cooperating with said portal means for gravitationally recovering a heavier-than-air gaseous refrigerant emanating from said portal and maintaining the refrigerant separated from the atmospheric gases;

f. means for conducting gaseous refrigerant from the trap means to a gaseous refrigerant liquifying means;

g. means for liquifying a gaseous refrigerant recovered in said traps; and

h. means for conducting and recirculating liquifie refrigerant from said refrigerant liquifying means to the liquid refrigerant contact means in said cooling zone.

2. An apparatus according to claim 1 wherein the liquid refrigerant contact means are a spray distributlOIl means.

3. An apparatus according to claim 1 wherein means are provided to produce supplemental gaseous refrigerant and introduce the same into said chamber.

- 4. An apparatus for continuous spray cooling of product units with liquid refrigerants in a cooling chamber which, under normal operation conditions, contains said liquid refrigerant in gaseous form at a positive pressure with respect to the atmosphere which apparatus comprises:

a. a cooling chamber essentially closed to the atmosphere and having inlet and outlet portal means for passage of product units into and out of the chamber, said chamber having direct communication to the surrounding atmosphere only at said portal means;

b. conveyor means for conducting product units through said chamber via the inlet and outlet means;

c. spray means for contacting product units with liquid refrigerant while said product units are in transit through said chamber;

d. trough-like recovery trap means adjacent to, below and cooperatively associated with said inlet and outlet means for gravitational recovery of a heavier-than-air gaseous refrigerant emanating through said portal from said chamber and maintaining said gaseous refrigerant separated from the atmosphere;

e. conduit means for conducting gaseous refrigerant from the trap means to a gaseous refrigerant liquifying means;

f. means cooperating with said conduit means for liquifying a gaseous refrigerant recovered in said traps; and

conduit means forconducting and recycling .a liquified refrigerant from the gas liquifying means to the spray contacting means.

5. An apparatus according to claim 4 wherein temperature sensor means are provided in said chamber and inter-connected with a liquid refrigerant supply control means to control the quantity of liquid refrigerant conducted to said liquid refrigerant contact means.

6. An apparatus according to claim 4 which includes means for vaporizing liquid refrigerant and conduit means for conducting a stream of said vaporized gaseous refrigerant from the vaporizing means into the chamber.

7. An apparatus according to claim 6 wherein the outlet of the conduit means are positioned to discharge a gaseous refrigerant stream at a point adjacent a food conveyor inlet and outlet means of the chamber.

8. An apparatus according to claim 6 wherein control means are provided to regulate and coordinate the supply of liquid refrigerant to the liquid refrigerant contact means and the vaporizer means.

9. An apparatus according to claim 8 wherein the control means are responsive to a temperature sensor means in said chamber.

10. An apparatus according to claim 4 wherein means.

1 1. An apparatus according to claim 10 wherein said vestibule comprises a baffel element disposed above said conveyor portal and a trough shaped trap means shielded vestibule means associated with said trap 5 disposed below the P meansare provided at the conveyor inlet and outlet 

1. An apparatus for cooling of product units by contact with liquid refrigerant materials which are normally gaseous and heavier-than-air at ambient room temperature conditions in a cooling chamber which, under normal operation conditions, contains said refrigerant in gaseous form at a positive pressure with respect to the atmosphere which apparatus comprises: a. a cooling chamber essentially closed to the atmosphere having at least one portal means for introduction and removal of product units, said chamber having direct communication to the surrounding atmosphere only at said portal means; b. a cooling zone and refrigerant contact means within said chamber for contacting said products with liquid refrigerant; c. means for introducing liquid refrigerant into said cooling zone and to said contact means; d. conveyor means for conveying products into and out of said chamber and cooling zone; e. trough-like trap means located outside the cooling chamber adjacent to, below and cooperating with said portal means for gravitationally recovering a heavier-than-air gaseous refrigerant emanating from said portal and maintaining the refrigerant separated from the atmospheric gases; f. means for conducting gaseous refrigerant from the trap means to a gaseous refrigerant liquifying means; g. means for liquifying a gaseous refrigerant recovered in said traps; and h. means for conducting and recirculating liquified refrigerant from said refrigerant liquifying means to the liquid refrigerant contact means in said cooling zone.
 2. An apparatus according to claim 1 wherein the liquid refrigerant contact means are a spray distribution means.
 3. An apparatus according to claim 1 wherein means are provided to produce supplemental gaseous refrigerant and introduce the same into said chamber.
 4. An apparatus for continuous spray cooling of product units with liquid refrigerants in a cooling chamber which, under normal operation conditions, contains said liquid refrigerant in gaseous form at a positive pressure with respect to the atmosphere which apparatus comprises: a. a cooling chamber essentially closed to the atmosphere and having inlet and outlet portal means for passage of product units into and out of the chamber, said chamber having direct communication to the surrounding atmosphere only at said portal means; b. conveyor means for conducting product units through said chamber via the inlet and outlet means; c. spray means for contacting product units with liquid refrigerant while said product units are in transit through said chamber; d. trough-like recovery trap means adjacent to, below and cooperatively associated with said inlet and outlet means for gravitational recovery of a heavier-than-air gaseous refrigerant emanating through said portal from said chamber and maintaining said gaseous refrigerant separated from the atmosphere; e. conduit means for conducting gaseous refrigerant from the trap means to a gaseous refrigerant liquifying means; f. means cooperating with said conduit means for liquifying a gaseous refrigerant recovered in said traps; and g. conduit means for conducting and recycling a liquified refrigerant from the gas liquifying means to the spray contacting means.
 5. An apparatus according to claim 4 wherein temperature sensor means are provided in said chamber and interconnected with a liquid refrigerant supply control means to control the quantity of liquid refrigerant conducted to said liquid refrigerant contact means.
 6. An apparatus according to claim 4 which includes means for vaporizing liquid refrigerant and conduit means for conducting a stream of said vaporiZed gaseous refrigerant from the vaporizing means into the chamber.
 7. An apparatus according to claim 6 wherein the outlet of the conduit means are positioned to discharge a gaseous refrigerant stream at a point adjacent a food conveyor inlet and outlet means of the chamber.
 8. An apparatus according to claim 6 wherein control means are provided to regulate and coordinate the supply of liquid refrigerant to the liquid refrigerant contact means and the vaporizer means.
 9. An apparatus according to claim 8 wherein the control means are responsive to a temperature sensor means in said chamber.
 10. An apparatus according to claim 4 wherein shielded vestibule means associated with said trap means are provided at the conveyor inlet and outlet means.
 11. An apparatus according to claim 10 wherein said vestibule comprises a baffel element disposed above said conveyor portal and a trough shaped trap means disposed below the portal. 